The purpose of this chapter was to gain an understanding of the performance of a commercial Merino ewe flock that was grazing a perennial lupin-based pasture. The stand of perennial lupins evaluated in this trial had survived under sheep grazing, modest inputs of fertiliser and lime, and 600-650 mm of rain a year for 8 years prior to commencing measurements. This result, and the three decades of research at the nearby Mt John Trial Site in Tekapo (Scott, 1989, 1994, 2014), indicated that Merinos would graze perennial lupin and that the perennial lupin plants would recover after each grazing. However, the performance of ewes grazing these pastures needed to be benchmarked against those on conventional pasture options. This was then supported with monthly agronomic measurements that included nutritive values.
Animal performance
Ewe live weight did not experience large variability throughout for either pasture type over the three growing seasons (Figure 3.6, Figure 3.7 and Figure 3.8). For example, in 2011/12, ewes on the lupin pasture lost an average of 3 kg over the two-month summer period while the ewes in the control mob gained an average of 5 kg. In the 2012/13 and 2013/14 seasons, ewe live weight either remained unaffected or increased slightly over the summer period (Figure 3.7 and Figure 3.8). Seasonal changes in live weight are related to the balance of energy supply and demand. In practice, this is a function of the production of palatable feed and the stocking rate. In this study, the control mob was consistently shifted between different paddocks to match seasonal supply and demand. In comparison, the stocking rate of the lupin mob was not adjusted within the grazing seasons, which meant feed availability was a function of the pre-determined stocking rate and within season biomass productivity. This was reflected in the animal performance data, where reproductive performance and live weight improved as the stocking rate was reduced from 143 ewes in 2011/12 to 101 ewes in 2013/14.
The high energy demand of lactation means that losses in ewe live weight are expected under most grazing situations (Geenty and Sykes, 1986). During early lactation (September to December), ewes on the lupin pasture lost up to 12% of their bodyweight compared to 3% or less in control ewes. However, the lupin ewes maintained their live weight during the second stage of lactation (December to February) and had a mean live weight of 58 and 62 kg/head in February 2013 and 2014, respectively. In this study, the loss of live weight during lactation was minimal and did not affect ewe performance in following seasons, where differences in ewe live weight between the lupin and control mobs were minimised when both mobs grazed on a common pasture between
62 February and April (Figure 3.6, Figure 3.7 and Figure 3.8). Following common grazing in 2012/13 and 2013/14, ewes returned to their respective pastures for tupping, where the control ewes reached a mean tupping weight of 62 kg which was 2 kg more than ewes on the lupin pasture. Tupping weights of both mobs were similar to those reported by Anderson et al. (2014), near Omarama in the Mackenzie Basin, whose mixed-age Merino ewe flock had a tupping weight of 59.5 kg after autumn grazing of lucerne. Furthermore, the tupping weights of ewes on the lupin pasture were about 10% higher than the Merino NZ Benchmark Group (Table 3.4), which probably contributed to the advantage in lambing percentage seen the next spring.
Table 3.4 Performance of mixed-age (MA) Merino ewes grazing on the perennial lupin pasture at Sawdon Station, Tekapo, compared with data from the central South Island Merino New Zealand (NZ) Benchmark Group.
Parameter Sawdon lupins†
Merino NZ Benchmark Group*
(2014)
Tupping weight (MA ewes) 60.5 54.6
Lambing (%) 112 103
Lamb losses (scanning to tailing) (%) 25 25.3
Lamb weaning weight (kg; 100 day adjustedᵠ) 24.2 25.4
Lamb live weight produced/100 ewes (kg) 2710 2616
Greasy wool weight (kg) 4.64 5.3
Wool diameter (µm) 18.6 18.6
† = Average values of 2012/13 and 2013/14 seasons are used when available.
*= Merino NZ Benchmark Group contains 20 farmers who are South Island High Country Class 1 producers.
ᵠ = Lamb liveweight was adjusted based on average liveweight gain between the start of lambing and the liveweight measurement that was nearest to 100 days.
The live weight of lambs at tailing was similar in each of the three grazing seasons. A mean tailing weight of approximately 19 kg was observed in both pastures with differences of less than 1.5 kg in each of the seasons. However, lambs on the lupin pasture were growing at 30-70 g/day slower than those on the control pastures between tailing in December and weaning in February. This meant control lambs had reached a live weight of 31 kg while lupin lambs weighed 29 kg; similar to the lamb weaning weight of 29 kg in Anderson et al. (2014). The 100 day adjusted lamb live weight was 24.2 kg for lupin lambs, which was slightly lower than 25.4 kg for the Merino NZ Benchmark Group (Table 3.4).
When ewes were scanned in August, there was no evidence that the tupping weight differences of 2 kg between the lupin ewes and control ewes had affected reproductive performance, with both
63 mobs scanning at 150% in 2012 and 2013. At tailing, lambs on the lupin pasture appeared to have a slightly higher survival rate with a mean lambing percentage of 112% over both seasons compared with 105% for control pastures. It is possible that the lupin pasture provided greater shelter for newborn lambs than the control pastures. Lamb losses (scanning to tailing) of the lupin mob were comparable to that of the Merino NZ Benchmark Group at 25% (Table 3.4).
The ewes on the lupin pasture produced wool with similar characteristics to that produced by the ewes on the lucerne and other conventional pastures. The mean fibre diameter for ewes on the lupin pasture and control ewes was about 18.5 ʅm, which was the same as wool produced by Merino ewes from the Merino NZ Benchmark Group (Table 3.4). The average fleece weight of the lupin ewes was 0.3 kg lighter than the control ewes at shearing in September 2013 (Table 3.3). However, both mobs had heavier fleeces than the 4.06 kg produced by Class 1 South Island High Country farms between 2006 and 2014 (Lamb, 2015). Differences in fleece weight may have been caused by differences in forage quantity and quality between the lupin pasture and control pastures. However, there is insufficient evidence to either confirm or reject this theory.
Agronomic performance
The lupin pasture started growing during September each year and provided significant amounts of forage during lambing and lactation when the pasture was stocked at 13.5-16 ewes/ha. When herbage measurements were taken in the second (2012/13) and third (2013/14) growth seasons, the lupin pasture gained about 4500 kg DM/ha between the start of lambing in October and tailing in December. Paddocks that were set stocked gained an average of 3500 kg DM/ha between October and November, whilst the un-grazed paddock accumulated 6500 kg DM/ha, and had a total biomass of about 9000 kg DM/ha by November of both seasons. This compares with a nearby crop of lucerne that yielded 4500 kg DM/ha when it was cut for silage in the same month (2013, data not shown). Forage yield in the un-grazed lupin paddock (Paddock 1) was similar to those reported by Moot and Pollock (2014) at a nearby site at Glenmore Station, near Lake Tekapo, where perennial lupin-dominant plots had accumulated 9100 kg DM/ha by mid-December, which accounted for 80% of their total annual yield. That site had a pH of 5.0 and soluble Al was 5.0 mg/kg (Moir and Moot, 2014) which would be considered far less favorable than the soil pH of 6.0 and soluble Al levels of <0.5 mg/kg at Sawdon Station.
During the spring growth period, relative proportions of non-lupin species, reproductive stem, lupin lamina and petiole were the main contributors to herbage mass (Figure 3.9 and Figure 3.11). In the
64 un-grazed paddock, non-lupin species contributed 30% and 23% of yield by November 2012 and 2013, respectively. This was higher than the 10-20% contribution made by companion species in Moot and Pollock (2014). It is not surprising that there was a higher proportion of other species at Sawdon Station as the trial was established 8 years prior to that of Moot and Pollock (2014). Thus, it is likely that the stand would naturally progress to have a greater abundance of fine-rooted grass species which are responsive to increasing available soil nitrogen as a result of the grazed, legume- dominant pastures.
Pasture cover was highest in December of both grazing seasons (Figure 3.9 and Figure 3.11). However, cover was 13% higher in December of the second season (2013/14). Despite a higher December pasture cover, the summer grazing period reduced pasture cover to 3500 kg DM/ha by February 2014; which was 58% lower than the cover in February of the previous season. Given that stocking rate was 20% higher in the first season, this result suggests that perennial lupin maintained active growth for a longer period in the 2012/13 season and/or senescence was delayed. This is further supported by the botanical composition data, where the abundance of lupin leaf was 10% higher in February of the first grazing season. Given that mean temperature and PET remained similar in both seasons; it seems likely that improved growth resulted from the additional 140 mm of rainfall between September 2012 and February 2013 (Figure 3.3).
Between December 2012 and March 2013, sheep selectively grazed lupin lamina which resulted in consistent decreases in lamina proportion at monthly measurements (Figure 3.10). The proportion of green components comprising yield consistently decreased from March until grazing ceased in May. During this period, the mean herbage mass declined linearly from 6300 kg DM/ha to 4500 kg DM/ha, where dead material represented 90% of the herbage on offer. The senescence of lupin stem and reduced palatability of other species caused an apparent increase in consumption of green lupin leaf material whose yield contribution decreased from about 30% in March to 4% in May of both seasons (Figure 3.10 and Figure 3.12). Increased grazing preference for lupin leaf material would seem logical given the large proportion of unpalatable dead components on offer during the autumn grazing periods.
Lupin lamina and flower had the highest ME, DMD and CP values in the 2012/13 and 2013/14 growing seasons (Figure 3.13 and Figure 3.14). In both seasons, lamina had a mean CP concentration of 28.2%, whilst ME ranged between 11.6 and 12.6 MJME/kg DM. These results were
65 consistent with those found for Russell lupin in Kitessa (1992), where the mean ME of lamina was 12.2-12.6 MJME/kg DM between October and January. This was also similar for DMD of lamina, where the mean of 2012/13 and 2013/14 was 82% compared with 85% for Kitessa (1992). The CP content of lamina was similar to values expected for green leaves of lucerne and clovers (Brown and Moot, 2004; Halim et al., 1989). For lupin flower, ME and CP were similar to lamina between November and January but had decreased substantially by February in both seasons. The decline in ME, DMD and CP was caused by the development of inflorescence and eventual hardening of seed pods (Plate 3.7). However, during autumn flowering, the nutritive value of flowers was similar to those found in spring. The consistently high nutritive value of both components helped to explain why lamina and flowers were the preferred lupin components for ewes and lambs (Figure 3.10 and Figure 3.12).
The nutritive value of lupin petiole was consistent between December and May, whilst stem material showed a general decline in ME, DMD and CP throughout the summer period (Figure 3.13 and Figure 3.14). For example, the ME of petiole was ~10 MJME/kg DM throughout both seasons, however, green stem declined from an ME of ~8.5 MJME/kg DM in December to ~6.8 MJME/kg DM in February. The decline in ME and CP of stem material appeared to be associated with the maturation of inflorescence in January. During this period, green stem began to senesce, but was not included in the dead fraction until it was brown in colour (Plate 3.8). Lupin petiole had a lower nutritive value than lamina but followed a similar pattern of disappearance, which suggested that its palatability was adequate for grazing.
Nutritive value results were similar to Kitessa (1992), which is the only other known study to have quantified the nutritive value of perennial lupin. This confirmed our confidence in the estimation values of the NIRS model (Appendix 1) so we could use it for further nutritive analysis in Chapter 4.
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